At present there is no direct clean-cut anatomic proof that the third, fourth and sixth pairs of cranial nerves are other than purely motor, and anatomic textbooks continue to speak of them only in this way. Anatomically, the inference that they carry kinesthetic sensibility as well is almost overwhelming, but the actual proof is not complete; physiologically, however, it may be regarded as proved.
The anatomic inference that these nerves mediate kinesthetic sense is based largely on the presence of neuromuscular and neurotendinous spindles 1 in the tendinous attachments and bellies of the extra-ocular eye muscles. In other portions of the body, these spindles have been shown 2 to be terminations of about two fifths of the fibers which run in "motor" nerves, the cells of origin of which are in posterior root ganglia. On the physiologic side, Sherrington 3 has published ingenious and incontrovertible proof that kinesthetic sense is
McLEAN AJ. AN ATTEMPT TO IDENTIFY THE CENTRAL CELLS MEDIATING KINESTHETIC SENSE IN THE EXTRINSIC EYE MUSCLES. Arch NeurPsych. 1927;17(3):285–302. doi:10.1001/archneurpsyc.1927.02200330002001
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